This invention relates to corrosion inhibition. More particularly, this invention relates to novel compositions which are useful for coating surfaces to provide temporary protection against corrosion.
There are numerous instances in industry where an easily-corrodable material (e.g. iron, steel, or other metal) is subjected to a variety of corrosive environments between the time when it is manufactured and the time when it is actually used as a raw material in the manufacture of an intended product. For example, sheet steel or iron, after it leaves the smelter and before it is incorporated by the purchaser into an end product, undergoes a considerable period (e.g. 3-12 months) of shipment, storage and handling. During such shipment, storage and handling, the metal may be subjected to environments which are capable of quickly corroding the surface of such material (e.g. environments such as air, air containing high humidity, air containing corrosive salts such as sodium chloride found in marine or industrial environments, rain, surface condensation, etc.). With increasing lengths of time before use, or with increasing severity of the environment to which the material is subjected before use, the greater is the degree of corrosion.
Consequently, it is usually necessary to remove the undesirable corrosion which is present on the surface of the material before such material may be satisfactorily used by the purchaser.
Unfortunately, this may be a very expensive and time-consuming process. Even more unfortunately, when the metal material is intended to be used in the manufacture of such products as painted or electroplated articles, even minute amounts of corrosion of the metal render such metal completely unsatisfactory for its intended purpose. In such event the metal must typically be returned to the smelter and replaced with new material. Where metal articles are shipped overseas, they are exposed to warm temperature, high humidity and corrosive salts in the atmosphere, and corrosion is a particularly severe problem.
In attempts to reduce or eliminate corrosion of metal during shipment and storage, various types of coatings and temporary protectants have been proposed. For example, it is possible to simply coat the metal with an oil, grease or wax. However, such types of coatings are not always effective, and they may be quite undesirable due to their flammability or oily nature. Furthermore, such types of coatings normally must be completely removed from the metal surface before the metal may be used in many manufacturing processes. Such removal naturally is time consuming and also requires the use of solvents, with attendant expense and pollution problems. Although the addition of conventional corrosion inhibiting materials to such oils, greases and waxes may render such types of coatings more effective, the problems associated with removal of the coating, when necessary, are not alleviated. Oil-based corrosion inhibiting compositions are described, for example, in U.S. Pat. No. 2,736,658 and U.S. Pat. No. 3,234,270.
Others have proposed the use of water soluble corrosion inhibiting materials. For example, in U.S. Pat. No. 2,918,390 there is proposed the treatment of metal with water soluble fatty acid amines, followed by treatment with a solution containing hexavalent chromium. In U.S. Pat. No. 3,017,353 there is described a composition which may be added to an aqueous phase or an oil phase. In U.S. Pat. No. 3,977,994 there is described an emulsion containing a mixture of certain amines and organic acids. In U.S. Pat. No. 3,625,859 there are described specific corrosion inhibiting salts which are said to be soluble in either a water-based system or an oil-based system. In U.S. Pat. No. 3,573,225 there is described an aqueous solution containing specified amounts of specific salts. In U.S. Pat. No. 3,553,150 there is described oil-based coating compositions containing amine alkyl acid phosphate salts and optionally containing carboxylic acids. In U.S. Pat. No. 3,846,071 there is described corrosion inhibiting compositions for use in oil wells containing an acidic phosphate ester of an oxyalkylated alcohol and cyclic amidines. None of such patents, however, describe the novel compositions of the present invention.